In the Chemical Mechanical Polishing process, the surface of a semiconductor wafer is removed by holding the face of the wafer against a moving polishing pad coated with slurry (Note: a pad is a material that protects the surface of the polishing tool and facilitates the movement of the slurry underneath the wafer, while conforming itself to the surface of the wafer). With time, the surface of the pad produces changes which affect the polishing rate, uniformity, and defect densities on the wafer. To overcome the degradation in the surface properties of the pad, many of the pads used in the CMP process require conditioning, i.e., abrading and washing the surface of the pad to expose a fresh surface for polishing. However, the bulk properties affecting the ability of the pad to planarize a wafer change as the pad becomes thinner. Polishing each wafer on a freshly generated pad reduces wafer to wafer variability; however, it is unrealistic to change pads after each wafer due to the cost and tool down time.
Etchants have been used in the art to selectively planarize certain areas of a wafer, as described for instance in U.S. Pat. No. 5,348,615 to Gupta. Yet, such an approach is inadequate for the more versatile chemical mechanical polishing process which ideally requires a combination mechanical abrasive components as well as the chemical component (chemical components are not solely etchants), as will be described hereinafter when describing the present invention, and more specifically for supplying slurry for CMP, which by their inherent nature are not limited to localized sub-micron scale areas.
Several attempts have been tried in the past to achieve the stated goal as, for instance, in U.S. Pat. No. 5,283,989 to Hisasue et al. Therein is described the formation of ice particles used as an abrasive agent. Such a material lacks the necessary properties required to incorporate the abrasive component normally found in slurry to become pad material to regenerate the pad itself.
Mechanical grinding has, oftentimes, been successfully used to regenerate the surface of an object, as described, e.g. in U.S. Pat. No. 4,785,587 to Reich et al. However, this approach suffers from serious drawbacks, as for instance, by introducing micro-fractures which render the surface of the wafer unusable. Further, mechanical grinding by itself possesses certain disadvantages by not being simultaneously combined with chemical reaction, as required by CMP. Moreover, a mechanical approach is unable by itself to regenerate the resurfacing material between uses and to liquefy the binder for the polishing abrasive during use, although it would be equally acceptable for the pad to remain solid during the polishing process and then be resurfaced and refreshed by a process unrelated to the wafer polish before subsequent wafers are processed.